The present invention relates to a detecting element for a detection cable intended to detect leaks of electrically nonconductive liquid. The invention also relates to a detection cable implementing such a detecting element and a detection system making it possible to use such detection cables. It also relates to a method for producing such a detecting element and a method for producing such a detection cable.
The detecting element comprises at least one detection member produced from a material which swells upon contact with said liquid and which is filled with electrically conductive particles, such that the detection member is conductive when it is not contaminated by said nonconductive liquid, and that it loses conductivity when it swells under the effect of said liquid.
According to the invention, this detection member is electrically connected to an electronic module, referred to as management module, which is arranged in order to detect the presence of said liquid by recording a decrease in the conductivity of said detection member, typically by means of an ohmic measurement.
The field of the invention is the detection of leaks of electrically nonconductive liquid, in particular by means of detection cables and for example for hydrocarbons.
The detection and location of leaks of electrically nonconductive liquid are carried out by means of systems or facilities using detection cables, which are arranged at sites in which leaks are likely to occur or flow.
The detection cables known are of different types. Some use variations in the electromagnetic properties occurring when a liquid seeps between several cable wires. These variations are detected for example by measuring impedance variations resulting from variations in the capacitance between these wires or the inductance of such a cable. This technology provides performances which would benefit from improvement, for example in terms of detection speed and/or sensitivity. Moreover, the measurement principle requires quite complex electronics, which makes it costly to produce and can represent a particular sensitivity to the environment.
Others use the change of shape of an element produced from a “reactive” conductive material, which swells upon contact with the liquid to be detected and thus makes it possible to establish an electrical contact between different elements which are normally separate.
In document U.S. Pat. No. 5,101,657 for example, two detection wires, each formed by a bare conductive wire, extend without touching inside the cable over its entire length, and are surrounded by an insulating perforated sheath. This perforated sheath is surrounded by a casing produced from this reactive material, itself contained in a perforated retention casing.
When the reactive material swells under the effect of the liquid to be detected, the retention casing prevents it from expanding towards the outside. Thus it expands towards the inside and comes into contact with the two detection wires by passing through the insulating perforated sheath. The contaminated reactive material thus makes an electrical short circuit between the two bare wires. The drop in electrical resistance between the two detecting wires is used in order to indicate the presence of the liquid to be detected.
These technologies also have drawbacks. For example, the structure is complex and requires a precise positioning of the wires in order to avoid the short circuits between the detection wires in the absence of liquid, which is a source of complexity during production. It would also be useful to reduce the detection time or the sensitivity according to the quantity of liquid to be detected.
In document U.S. Pat. No. 5,341,128, a linear sensor formed by two conductive elements connected at the end thereof has also been proposed. One of the elements is metallic and the other is a swellable material sensitive to hydrocarbons and including a conductive filler. The detection therefore uses an electrical power supply and a resistance indicator. However, these technologies have drawbacks, for example a particular sensitivity of the sensor in a difficult environment, and in which the problems of sensitivity and harsh or even dangerous environments are not managed.
An aim of the invention is to wholly or partially overcome the drawbacks of the state of the art. This includes for example increasing the speed of detection or the sensitivity in the case of small quantities of liquids, obtaining greater robustness, a simpler and more cost-effective production or a simpler and more flexible use.